Process for preparing bitumen-polymer compositions, application to these compositions of the obtention of coverings and mother solution of polymer usable for the obtention of the said compositions

ABSTRACT

Bitumen-polymer compositions are prepared, by mixing, at between 130° C. and 230° C., a bitumen with a styrene and conjugated diene copolymer and a sulphur source, the copolymer and the sulphur source being added to the bitumen either directly, or in the form of a mother solution in a hydrocarbon oil, then by maintaining the whole under stirring at between 130° C. and 230° C. for at least fifteen minutes. 
     By way of sulphur source is used 0.005 to 15% by weight, with respect to bitumen, one or several polymeric or not, cyclic or linear polysulphides, and especially ditertiododecyl or dinonyl pentasulphide. The bitumen-polymer compositions obtained can be used for the obtention of superficial road coverings and present a constant quality of its properties.

This is a division of application Ser. No. 502,827 filed June 9, 1983,now U.S. Pat. No. 4,554,313.

The present invention concerns a process for the preparation ofbitumen-polymer compositions. It also concerns the application ofcompositions obtained through this process to the production ofcoatings, and in particular superficial road coverings, and relates,furthermore, to a polymer mother solution for the obtention of saidcompositions.

It is known to use bituminous compositions as coverings for diversesurfaces and, especially, as superficial road coverings.

It is also known that various polymers can be added to the bitumens inorder to form bitumen-polymer type compositions, that present improvedmechanical properties with respect to the polymer-free bituminouscompositions. Examples of polymers suitable for the adding to thebitumens are, for instance, polyisoprene, butyl rubber, polyisobutene,ethylene and vinyl acetate copolymers, polymethacrylate,polychloroprene, random or block copolymers of styrene and a conjugateddiene. Among these latter random or block copolymers of styrene and aconjugated diene and especially styrene and butadiene or styrene andisoprene, are known as being particularly efficient, since they dissolvevery easily in bitumens and confer on the said bitumens very goodmechanical properties and particularly excellent visco-elasticityproperties. Furthermore, it is known to increase the stability of thebitumen-polymer compositions, and thus to widen their field ofapplication, by realizing a chemical coupling between the polymer andthe bitumen.

This can be carried out, for example, as described in French Pat. No.76.39233 (published under No. 2.376.188) filed Dec. 28, 1976, by mixing,at a temperature comprised between 130° C. and 230° C., bitumen with, byweight of bitumen, 2 to 25% of a styrene and conjugated diene random orblock copolymer and 0.1 to 3% chemically non-linked sulfur, and bymaintaining the resulting mixture at the temperature mentionedherein-above and under stirring for at least twenty minutes.

In such a process, which involves a direct solubilisation of the polymerin the bitumen, a suitable homogeneity is only achieved after a periodof stirring of the mixture of bitumen, polymer and sulphur at hightemperatures, comprised between 130° C. and 230° C. and most often atabout 150° C. to 200° C. which increases progressively with the quantityof polymer to be incorporated into the bitumen and needs, in themajority of cases, about 2 to 4 hours.

This relatively long homogeneisation period and the consequentsubstantial calorific energy consumption, reflect unfavorably on thecost price of the operation. Furthermore, the compositions obtainedthrough this process, although having acquired useful mechanicalproperties, possess high viscosities, that make them difficult to spreadusing standard distributors equipping the spreading material.

In order to facilitate the preparation of bitumen-polymer compositions,for which a styrene and conjugated diene random or block copolymer islinked to the bitumen by using chemically non-linked sulphur as thecoupling agent, and to render the said compositions directly utilisableby classic spreading means, it has been proposed, as described in FrenchPat. No. 78.18534 (published under No. 2.429.241) filed June 21, 1978 tosimultaneously incorporate into the bitumen the copolymer and thesulphur in the form of a mother solution of these two products in asolvent constituted by a hydrocarbon oil having a distillation range atatmospheric pressure comprised between 150° C. and 250° C., the saidmother solution being prepared at a temperature comprised between 80° C.and 160° C. and being added to the bitumen at temperatures between about130° C. and 230° C.

The dissolution of the copolymer in the hydrocarbon fraction is quickerand easier than the direct dissolution of the said copolymer in thebitumen, and there is a consequent saving of time and energy to obtainthe final bitumen-polymer composition. Furthermore a fluidifiedcomposition is obtained directly that satisfies the viscosityrequirements necessary for the obtention of good spreading conditions.

In the process described in French Pat. No. 76.39233, as in the-improvedprocess of French Pat. No. 78.18534, the use of chemically nonlinkedsulphur, especially sulphur flower or alpha crystallized sulfur, ascoupling agent of the copolymer to the bitumen presents certaindrawbacks.

Indeed, at the moment of direct incorporation of the copolymer and thesulphur into the bitumen, it is difficult to distribute the sulphurthroughout the mixture in a homogenous manner, and in the same way, toaccordingly carry out regularly the chemical grafting of the copolymerto the bitumen and cross-linking the chains of the copolymers betweenone another. Furthermore, when the copolymer and the sulphur areincorporated into the bitumen using the mother solution technique, localover-vulcanisations of the polymer can occur, during the preparation ofthe mother solution, which subsequently unfavorably influence theproperties of the final bitumen-polymer composition. Furthermore, inthis mother solution, the sulphur can recrystallize and form sedimentwith time, especially after prolonged storage at ambient temperature,which thus renders difficult the obtention of a product of constantquality.

It has now been found that it is possible to eliminate the drawbacksinherent in the use of solid sulphur in preparation techniques ofbitumen-polymer compositions of the same type as those proposed in theabove-mentioned French patents, by replacing the said sulphur by apolysulphide, and especially by a dihydrocarbyl polysulphide.

Such a polysulphide is more easily soluble in the bitumen or in thehydrocarbon oil fraction constituting the solvent of the mother solutionthat the finely divided solid sulphur, and furthermore, the quantity ofradicular sulphur that forms from polysulphide, is easier to controlthan that produced from solid sulphur, which allows a better control ofgrafting the copolymer to the bitumen and the cross-linking of thecopolymers between one another, with, as a result, the obtention of abitumen-polymer composition presenting a constant quality in itsproperties. This constitutes an important advantage during repair worksof road coverings, which necessitate quantities of bitumen-polymercomposition of several thousand tons to be prepared in severalfractions.

The invention thus concerns a process for the preparation ofbitumen-polymer compositions, in which is produced, at a temperaturecomprised between 130° C. and 230° C., a mixture of bitumen with astyrene and conjugated diene copolymer, used in a quantity ranging from0.5 to 15% by weight bitumen, and a sulphur source, and the mixture thusobtained, is maintained under stirring, within the said temperaturerange, during a period of at least 15 minutes, the said process beingcharacterized in that, as sulphur source, is used 0.005 to 15% byweight, with respect to the bitumen, of a polysulphide or apolysulphides mixture having the general formula:

    R.sub.1 --(S).sub.m --R--(S).sub.m).sub.x R.sub.2

in which:

R₁ and R₂ each designate a C₁ to C₂₀ saturated or unsaturated monovalenthydrocarbon radical or are linked together in order to constitute a C₁to C₂₀ saturated or unsaturated divalent hydrocarbon radical forming acycle with the other groups of atoms associated in the formula;

R is a C₁ to C₂₀ saturated or unsaturated, divalent hydrocarbon radical;

--(S)_(m) -- represents divalent groups each formed from "m" sulphuratoms, "m" able to be different from one of the said groups to the otherand designating whole numbers ranging from 1 to 6 with at least one of mbeing equal to or above 2; and

x represents a whole number ranging from 0 and 10.

In the formula shown above, the C₁ to C₂₀ monovalent hydrocarbonradicals, R₁ and R₂ as well as the C₁ to C₂₀ divalent hydrocarbonradical, are especially selected from among the aliphatic, alicyclic oraromatic radicals. When the R₁ and R₂ radicals are connected to oneanother to constitute a C₁ to C₂₀ divalent hydrocarbon radical forming acycle with the other groups of atoms associated in the formula, the saiddivalent radical is similar to radical R and can also be of thealiphatic, alicyclic, or aromatic type. In particular, radicals R₁ andR₂ are identical and selected from among C₁ to C₂₀ alkyl radicals, forexample, ethyl, propyl, hexyl, octyl, nonyl, decyl, linear dodecyl,tertiododecyl, hexadecyl, octadecyl, and C₆ to C₂₀ cycloalkyl and arylradicals, especially benzyl, phenyl, tolyl, cyclohexyl, whereas radicalR or the divalent radical formed by the association of R₁ and R₂ areselected among the C₁ to C₂₀ alkylene radicals, or C₆ to C₂₀cycloalkylene or arylene radicals such as phenylene, tolylene andcyclohexylene.

Polysulphides for use according to the present invention are, inparticular, those defined by the formula:

    R.sub.1 --(S).sub.n --R.sub.2

in which:

R₁ and R₂ each designate a C₁ to C₂₀ saturated or unsaturated monovalenthydrocarbon radical, or are joined together in order to form a C₁ to C₂₀divalent radical similar to R, R₁, R₂ and R having the previouslyindicated meaning;

--(S)_(n) -- represents a divalent group formed by a chaining of nsulphur atoms;

n being an integer ranging from 2 to 6.

Preferred polysulphides have the general formula:

    R.sub.3 --(S).sub.p --R.sub.3

in which:

R₃ designates a C₆ to C₁₆ alkyl radical; and,

--(S)_(p) -- represents a divalent grouping formed by the chaining of psulphur atoms;

p being an integer ranging from 2 to 5.

Examples of such polysulphides are especially dihexyl disulphide,dioctyl disulphide, dihexadecyl disulphide, dihexyl trisulphide, dioctyltrisulphide, dinonyl trisulphide, ditertiododecyl trisulphide,dihexadecyl trisulphide, dioctyl tetrasulphide, dinonyl tetrasulphide,ditertiododecyl tetrasulphide, dihexadecyl tetrasulphide, dihexylpentasulphide, dioctyl pentasulphide, dinonyl pentasulphide,ditertiododecyl pentasulphide, dihexadecyl pentasulphide, dioctyldisulphide, didodecyl disulphide, dihexyl tretrasulphide.

Other polysulphides, that can be used according to the invention, are,for example, diphenyl trisulphide, dibenzyl trisulphide, diphenyltetrasulphide, orthotolyl tetrasulphide, dibenzyl tetrasulphide,dibenzyl pentasulphide, diallyle pentasulphide, tetramethyltetrathiane.

The quantity of polysulphide, that can range from 0.005% to 15% byweight of bitumen, preferably represents 0.1% to 5% by weight.

The bitumen, that constitutes the major part of the bitumen-polymercompositions according to the invention, is selected from among thevarious bitumens having a penetration, defined according to Frenchstandard NFT 66004, comprised between 5 and 500 and preferably 20 and400. Such bitumens can be, in particular, direct distillation bitumens,or blown or semi-blown bitumens having a penetration comprised withinthe ranges mentioned herein-above.

The styrene and conjugated diene copolymer, used in the preparation ofthe bitumen-polymer composition, is advantageously selected from amongthe following random or block copolymers: styrene and butadiene, styreneand isoprene, styrene and chloroprene, styrene and carboxylatedbutadiene and styrene and carboxylated isoprene copolymers. The styreneand conjugated diene copolymer, and in particular each of theaboved-mentionel copolymers, has a styrene content by weight rangingpreferably from 15% to 40%. The average viscosimetric molecular weightof the styrene and conjugated diene copolymer, and especially that ofthe copolymers mentioned above, may be advantageously comprised between30.000 and 300.000 and located preferably between 70.000 and 200.000.

The styrene and conjugated diene copolymer is preferably selected fromamont the following di- or triblock copolymers: styrene and butadiene,styrene and isoprene, styrene and carboxylated butadiene, styrene andcarboxylated isoprene copolymers having a styrene content and molecularweight comprised within the range mentioned herein-above.

The preferred quantity of copolymer added to the bitumen is comprisedbetween 0.7% and 10% by weight of bitumen.

In a preferred embodiment of the invention, the copolymer and thepolysulphide are incorporated into the bitumen in the form of a mothersolution of these two products in a solvent consisting of a hydrocarbonoil, that presents a distillation range at atmospheric pressure,determined according to U.S. standard ASTM D 88-67, comprised between100° C. an 450° C. and preferably between 150° C. and 370° C.

This hydrocarbon oil, that can be especially a petroleum cut having anaromatic character, a petroleum cut having a naphteno-paraffiniccharacter, a petroleum cut having a naphteno-aromatic character, a coaloil or an oil of vegetable origin, is sufficiently "heavy" in order tolimit the evaporation at the moment of the addition of the mothersolution to the bitumen and at the same time sufficiently "light" to beeliminated at maximum after spreading the bitumen-polymer compositioncontaining it in such a way as to recover the same mechanical propertiesthat would have presented, after hot spreading, the bitumen-polymercomposition, prepared without using the mother solution technique.

The mother solution is prepared by contacting the ingredients comprisingit, namely hydrocarbon oil acting as solvent, copolymer, andpolysulphide, under stirring, at temperatures comprised between 20° and170° C. and more particularly between 40° and 120° C., during sufficienttime, for example about 30 minutes to about 90 minutes, in order toobtain a complete dissolution of the copolymer and polysulphide inhydrocarbon oil.

The respective copolymer and polysulphide concentrations in the mothersolution can vary fairly widely in function especially of the nature ofthe hydrocarbon oil used to dissolve the copolymer and polysulphide.Therefore, the respective quantities of copolymer and polysulphide canadvantageously represent 5% to 40% and 0.1 to 15% by weight ofhydrocarbon oil. A preferred mother solution contains, by weight ofhydrocarbon oil used as solvent, 10 to 35% copolymer and 0.5 to 5%polysulphide.

When the compositions according to the invention are directly formedfrom the bitumen, copolymer and polysulphide, it is preferable tooperate by contacting the copolymer with the bitumen in selectedproportions, at a temperature comprised between 130° C. and 230° C. andunder stirring, during a period, generally from 20 minutes or more toseveral hours, in order to form a homogenous mixture, then by adding thepolysulphide to the mixture obtained and maintaining the whole understirring at a temperature comprised between 130° C. and 230° C., forexample, corresponding to contacting temperature of the copolymer withthe bitumen, during a period at least equal to 15 minutes, and generallyranging from 15 to 90 minutes, to allow the polysulphide to liberate theradicular sulphur and to allow the radicular sulphur thus produced toinitiate on the one hand the grafting of the copolymer to the bitumenand, on the other hand, the cross-linking between themselves of thechains of the copolymer.

The quantities of the copolymer contacted with the bitumen andpolysulphide thereafter added to the homogenous mixture of the bitumenand said copolymer are selected to be comprised within the rangeshereinabove specified for these quantities.

To prepare the bitumen-polymer compositions according to the presentinvention, by using the mother solution technique, the mother solutionof the copolymer and the polysulphide is mixed with the bitumen,operating at a temperature comprised between 130° and 230° C. and understirring, this being carried out, for example, by adding the mothersolution to the bitumen maintained under stirring at a temperaturebetween 130° C. and 230° C., then the resulting mixture is maintainedunder stirring at a temperature comprised between 130° C. and 230° C.,for example, at the temperature used for adding the mother solution tothe bitumen during a period at least equal to 15 minutes, and generallyranging from 15 to 90 minutes, to allow through the biais of thepolysulphide, the grafting of the copolymer to the bitumen asphaltenesand the cross-linking between themselves of the chains of the saidcopolymer.

The quantity of mother solution mixed to the bitumen is selected tosupply the desired quantities, with respect to the bitumen, of thiscopolymer and polysulphide, the said quantities being in the rangesdefined herein-above.

One form of realisation that is especially preferred for the preparationof the bitumen-polymer composition according to the present invention,through use of the mother solution technique consists in contacting, ata temperature comprised between 130° C. and 230° C. and under stirring,from 80 to 95% by weight bitumen with 20 to 5% by weight mothersolution, this mother solution containing by weight of the hydrocarbonoil acting as the solvent, 10 to 35% styrene and conjugated dienecopolymer and 0.5 to 5% polysulphide, then in maintaining the thusobtained mixture under stirring at a temperature comprised between 130°C. and 230° C., and preferably at the temperature prevailing duringcontacting the bitumen and the mother solution, for a period of at least15 minutes, and preferably comprised between 20 and 60 minutes.

The bitumen-polymer compositions obtained through the process accordingto the invention can be used for producing various coverings, andespecially superficial road coverings. For this application,particularly, the bitumen-polymer compositions according to theinvention prepared by the mother solution technique are especiallyadapted, since they can be directly used with standard spreading means.

The invention is illustrated by the following non-limitative examples.

The rheological and mechanical characteristics of the bitumens orbitumen-polymer compositions to which reference is made in theseexamples are the following:

penetration: expressed in 1/10 mm and measured in accordance withstandard NFT 66004.

softening point: expressed in °C. and determined by Ball and Ring test(B & A test defined by standard NFT 66008).

Fraass point: fragility point, expressed in °C. and determined inaccordance with standrad IP 80/53.

rheological characteristics by elongation (standard NFT 46002)

threshold strain α_(s) . . . in bars

threshold elongation ε_(s) . . . in %

strain at rupture α_(r) . . . in bars

elongation at rupture ε_(r) . . . in %

cinematic viscosity: expressed in stokes and determined according toFrench standard NFT 60100.

pseudo-viscosity expressed in seconds and determined in accordance withFrench standard NFT 66005.

EXAMPLE 1

Preparation of a bitumen-polymer composition according to the inventionthrough direct incorporation of the copolymer and the polysulphide tothe bitumen.

Operating at 170° C. under stirring, 1,000 parts by weight of a directdistillation bitumen having a penetration of 82, "ball and ring"softening point of 48° C., Fraass point equal to -18.5° C. and acinematic viscosity at 160° C. of 1.7 stokes, with 31 parts by weight ofa di-block styrene and butadiene copolymer having an averageviscosimetric molecular weight equal to about 75.000 and containing 25%by weight styrene.

After 3 hours 20 minutes of mixing under stirring, a homogenous mass isobtained.

To this mass maintained at 170° C., 7.3 parts by weight ditertiododecylpentasulphide are added, and the whole is again stirred for thirtyminutes in order to form the composition according to the invention.

Table I shows the principle characteristics of the bitumen-polymercomposition thus obtained both before and after having subjected it tothe aging test called "Rolling Film Oven Test" defined in ASTMD 2872,modified in order to bring the period of heat treatment to 150 minutes.The compositions according to the invention before and after the agingtest are designated respectively by "Product Ia1" and "Product Ia2".

Table I also gives the corresponding characteristics of the startingbitumen before and after the aging test (respectively "Product Ib1" and"Product Ib2").

It is noted from the values indicated on table I that the use ofditertiododecyl pentasulphide, as the sulphur supply, leads to abitumen-polymer composition, the elastomer characteristics of whichdifferentiate it very clearly from the bitumen (cf. the traction testresults). Furthermore, the stability to aging of the bitumen-polymercomposition obtained is susbstantially improved with respect to thatobserved for the pure bitumen.

EXEMPLE 2

Preparation of a bitumen-polymer composition according to the inventionthrough the mother solution technique.

(a) Preparation of the mother solution

Operating occurs in a stainless steel reactor provided with a stirrerand a double jacket adapted to be through-crossed by a heat-carryingfluid.

The hydrocarbon oil used as solvent to form the mother solution was apetroleum cut having a naphteno/aromatic character presenting thefollowing characteristics:

ASTM initial distillation point equal to 176° C.,

ASTM final distillation point equal to 352° C., (measured according tostandard ASTM D 86-67).

flash point (French Luchaire standard NFT 60103) of 79° C.,

volumic mass (U.S. standard ASTM D 1657-64) equal to 0.956.

                                      TABLE I                                     __________________________________________________________________________    Characteristics                                                               penetration                                                                              softening                                                                            Fraass                                                                             Traction tests                                              at 25° C.                                                                    point  point                                                                              Temp.                                                                             speed                                                                              σs                                                                         σr                                                                         εs                                                                      εr                            Product                                                                            (1/10 mm)                                                                           B & R (°C.)                                                                   (°C.)                                                                       (°C.)                                                                      mm/mn                                                                              bars                                                                             bars                                                                             % %                                     __________________________________________________________________________    I a 1                                                                              68    56     -19.5                                                                               20 500  1.4                                                                              0.6                                                                              25                                                                              >900                                                         -10  10  29 10.5                                                                             15                                                                               350                                  I a 2                                                                              49    59     -17   20 500  1.7                                                                              0.9                                                                              15                                                                              >900                                                         -10  10  32 13 15                                                                               300                                  I b 1                                                                              82    48     -18.5                                                                               20 500  1.2                                                                              0  15                                                                              >900                                                         -10  10  FRAGILE                                       I b 2                                                                              51    50     -15   20 500  1.8                                                                              0  15                                                                              >900                                                         -10  10  FRAGILE                                       __________________________________________________________________________

233 parts by weight of the petroleum cut were introduced into thereactor and this petroleum cut was heated, under stirring, to atemperature of about 100° C. through circulation of a hot fluid in thedouble jacket of the reactor.

While maintaining thus temperature, and under stirring, 13 parts byweight of the pentasulphide used in Example 1 and 54 parts by weight ofa powder, containing 2% by weight silica to prevent lumping, of adiblock styrene and butadiene copolymer containing 25% styrene andpossessing an average viscosimetric molecular weight of about 75.000were introduced.

After one hour's stirring at about 100° C., a homogenous and fluidsolution at ordinary temperature is obtained characterized by thefollowing cinematic viscosity values:

    ______________________________________                                        cinematic viscosity measured                                                                      12.10 stokes                                              at 50° C.                                                              cinematic viscosity measured                                                                       2.92 stokes                                              at 100° C.                                                             ______________________________________                                    

This solution constituted the mother solution used for the preparationof the bitumen-polymer composition.

(b) Preparation of the bitumen-polymer composition

Into an oven equipped with stirrers and provided with steam reheaters,is pumped at 170° C., 1,700 parts of a direct distillation bitumenhaving the following initial physical properties:

softening point (B & R test) . . . 48° C.

Fraass point . . . -18.5° C.

penetration . . . 82 1/10 mm

cinematic viscosity at 160° C. . . . 1.70 stokes

To the contents of the oven, maintained at 170° C. under stirring, isthereafter added 300 parts of the mother solution prepared as describedherein-above.

After 30 minutes stirring at 170° C., a bitumen-polymer fluidcomposition presenting a dynamic viscosity at 160° C. equal to 0.098Pa.s., i.e. a viscosity comparable to that of a bitumen having apenetration within the range 180-220, and able to be charged directly ina standard medium pressure spreading distributor. Table II shows theproperties of the bitumen-polymer composition thus obtained before andafter having subjected it to thermal treatment consisting in bringing to50° C. a film of 1 mm thickness of the bitumen-polymer composition andmaintaining the said film at this temperature for 15 days, this testallowing the simulation of the evolution of the product during one yearon the road. The bitumen-polymer is designated by "Product IIa1" beforethermal treatment and by "Product IIa2" after thermal treatment. TableII also shows, by way of comparison, before and after the herein-abovementioned thermal treatment, the corresponding characteristics of thestarting bitumen fluidified by 12% by weight, with respect to thebitumen, of the solvent used to constitute the mother solution (ProductIIb1 and Product IIb2 respectively), and of a bitumen-polymercomposition prepared in a way similar to that described in Example 2 butwithout polysulphide (Product IIc1 and

                                      TABLE II                                    __________________________________________________________________________    Characteristics                                                                                     viscosity                                               penetration                                                                              softening                                                                            Fraass                                                                            (Rheomat)                                                                           Pseudo                                                                             traction tests                                    at 25° C.                                                                    point  point                                                                             at 160° C.                                                                   viscosity                                                                          Temp.                                                                             speed                                                                              σs                                                                         σr                                                                         εs                                                                      εs                  Product                                                                            (1/10 mm)                                                                           B & R (°C.)                                                                   (°C.)                                                                      (Poise)                                                                             (s)  (°C.)                                                                      mm/mn                                                                              bars                                                                             bars                                                                             % %                           __________________________________________________________________________    II.a.1                1.18  148  -10 500  7.2                                                                              2.4                                                                              18                                                                              > 900                       II.a.2                                                                              82   52     -19 3.5         20 500  0.75                                                                             0.5                                                                              20                                                                              >900                                                         -10  10  18 7  20                                                                              450                         II.b.1                0.7   60   -10 500  FRAGILE                             II.b.2                                                                             105   47     -13 2.6         20 500  0.5                                                                              0  15                                                                              800                                                          -10  10  FRAGILE                             II.c.1                0.81  84   -10 500  6.3                                                                              0  15                                                                              300                         II.c.2                                                                             102   48     -15 2.5         20 500  0.6                                                                              0  15                                                                              900                                                          -10  10  FRAGILE                             __________________________________________________________________________

Product IIc2).

In the designation of the product, indice 1 define the compositionsbefore thermal treatment whereas indice 2 define the compositions afterthermal treatment.

As can be seen from the comparison of the results shown in Table II, theuse of ditertiododecyl pentasulphide, as the sulphur source, in themother solution technique leads to the obtention of a fluidifiedbitumen-polymer composition having elastomeric characteristics. Afteraging, the product gives a residual binder, the properties of which aresimilar to those of the bitumen-polymer composition obtained in Example1 by incorporating the polymer and the polysulphide to the bitumenwithout using the mother solution.

EXAMPLES 3 TO 8

Preparation of bitumen-polymer compositions according to the inventionthrough the mother solution technique.

Operating occurs as described in Example 2 with, however, certainvariations that are defined herein-below, the other operating conditionsbeing those of Example 2.

In Example 3, the mother solution was formed from 243 parts by weight ofthe petroleum cut, 53.5 parts of the diblock styrene and butadienecopolymer, and 3.5 parts by weight polysulphide.

In Example 4, the copolymer consisted of a diblock styrene and isoprenecopolymer containing 22% by weight styrene and having an averagevicosimetric molecular weight of about 78.000.

In Example 5, the copolymer consisted of a diblock styrene andcarboxylated butadiene copolymer containing 25% by weight styrene andpresenting an average viscosimetric mass of about 76.000.

In Example 6, the polysulphide consisted of dinonyl pentasulphide havinga molecular weight equal to 414.

In Example 7, the polysulphide was the same as that used in Example 6and the mother solution was formed from 240 parts by weight of thepetroleum cut, 54 parts by weight of the copolymer, and 6 parts byweight of polysulphide.

In Example 8, the polysulphide was the same as that used in Example 6,and the mother solution was formed from 243 parts by weight of thepetroleum cut, 54 parts by weight of the copolymer, and 3 parts byweight of polysulphide.

Table III gives the characteristics of the bitumen-polymer compositionsthus obtained, before and after having subjected them to the thermaltreatment defined in Example 2.

The bitumen-polymer compositions before thermal treatment are designatedby "Product Ya2", Y representing the number of the Example in Romannumerals.

                                      TABLE III                                   __________________________________________________________________________                               viscosity                                                    penetration                                                                         softening                                                                            Fraass                                                                            (Rheomat)                                                                           Pseudo                                                                             Traction tests                                    at 25° C.                                                                    point  point                                                                             at 160° C.                                                                   viscosity                                                                          Temp.                                                                              speed                                                                              σs                                                                          σs                                                                         εs                                                                       εs          Example                                                                            Product                                                                            (1/10 mm)                                                                           B & R (°C.)                                                                   (°C.)                                                                      (Poise)                                                                             (s)  (°C.)                                                                       mm/mn                                                                              bars                                                                              bars                                                                             %  %                   __________________________________________________________________________    3    III.a.1               0.94  120  -10  500  7.3 0.33                                                                             15 450                      III.a.2                                                                            90    50     -20 3.1         20  500  0.6 0.4                                                                              20 >900                                                      -10   10  15  5  20 400                 4    IV.a.1                1.35  160  -10  500  8.1 2.8                                                                              15 >900                     IV.a.2                                                                             78    54     -19 4           20  500  0.9 0.6                                                                              15 700                                                       -10   10  22  8  15 200                 5    V.a.1                 1.25  175  -10  500  7.6 3.5                                                                              20 > 900                    V.a.2                                                                              75    55     -21 4.1         20  500  1   0.7                                                                              20 900                                                       -10   10  25  9.5                                                                              15 660                 6    VI.a.1                1.25  138  -10  500  5.9 2.45                                                                             18 >900                     VI.a.2                                                                             80    55     -21 4.6         20  500  1.2 1  20 >900                                                      -10   10  24  10.5                                                                             20 500                 7    VII.a.1               1.05  115  -10  500  6.6 1.2                                                                              18 >900                     VII.a.2                                                                            87    55     -18 3.8         20  500  1   0.3                                                                              25 >900                                                      -10   10  20  6.3                                                                              15 270                 8    VIII.a.1              0.98  104  -10  500  7.4 0.5                                                                              18 560                      VIII.a.2                                                                           105   49     -20 2.5         20  500  0.9 0.15                                                                             25 900                                                       -10   10  17  4.2                                                                              25 100                 __________________________________________________________________________

We claim:
 1. A polymer mother solution for the preparation of bitumen-polymer compositions, comprising a hydrocarbon oil having a distillation range, at atmospheric pressure comprised between 100° C. and 450° C., and in solution in the oil, from about 5 to 40% by weight of the oil of a styrene conjugated diene copolymer and from about 0.1 to 15% by weight of the oil of a sulphur source, wherein the sulphur source comprises a polysulphide of the formula:

    R.sub.1 --(S).sub.m --R--(S).sub.m).sub.x R.sub.2

wherein: R₁ and R₂ are each independently a C₁ to C₂₀ saturated monovalent hydrocarbon radical, a C₁ to C₂₀ unsaturated monovalent hydrocarbon radical or R₁ to R₂ can be linked to form a C₁ to C₂₀ saturated divalent hydrocarbon radical or a C₁ to C₂₀ unsaturated divalent hydrocarbon radical; R is a C₁ to C₂₀ saturated divalent hydrocarbon radical or a C₁ to C₂₀ unsaturated divalent hydrocarbon radical; --(S)_(m) is a divalent group of sulphur atoms, wherein m can be different for each group and represents a whole number of from 1 to 6 with at least m in one group being at least 2; and x represents a whole number ranging from 0 to
 10. 2. A mother solution according to claim 1, wherein the polysulphide is defined by the formula

    R.sub.1 --(S).sub.n --R.sub.2

wherein R₁ and R₂ each represent a C₁ to C₂₀ saturated monovalent hydrocarbon radical or a C₁ to C₂₀ unsaturated hydrocarbon radical or R₁ and R₂ can be linked together to form a C₁ to C₂₀ saturated divalent hydrocarbon radical or an unsaturated divalent hydrocarbon radical; --(S)_(n) -- represents a divalent group of n sulphur atoms; n being an integer of from 2 to
 6. 3. A mother solution according to claim 1 or 2, wherein R₁ and R₂ are identical and selected from C₁ to C₂₀ alkyl radicals, C₆ to C₂₀ aryl radicals and C₆ to C₂₀ cycloalkyl radicals or are linked together to form a C₁ to C₂₀ divalent alkylene radical, a C₆ to C₂₀ cycloalkylene or a C₆ to C₂₀ arylene radical, and wherein R is selected from C₁ to C₂₀ alkylene radicals, C₆ to C₂₀ cycloalkylene radicals and C₆ to C₂₀ arylene radicals.
 4. A mother solution according to claim 2, wherein the polysulphide has the formula:

    R.sub.3 --(S).sub.p --R.sub.3

wherein: R₃ is a C₆ to C₁₆ alkyl radical; and --(S)_(p) -- represents a divalent group of p sulphur atoms, p being an integer of from 2 to
 5. 5. A mother solution according to claim 1 or 2, prepared by contacting the hydrocarbon oil, copolymer and polysulphide with stirring, at a temperature between 40° and 120° C.
 6. A road surface covering comprising a bitumen-polymer composition prepared by(a) forming a mixture of a bitumen, from about 0.5 to 15% by weight of the bitumen of a styrene-conjugated diene copolymer and from about 0.005 to 15% by weight of the bitumen of a polysulfide of the formula:

    R.sub.1 --(S).sub.m (R--(S).sub.m).sub.x R.sub.2

wherein R₁ and R₂ are each independently a C₁ to C₂₀ saturated monovalent hydrocarbon radical or a C₁ to C₂₀ unsaturated monovalent hydrocarbon radical, or R₁ or R₂ can be linked to form a C₁ to C₂₀ saturated divalent hydrocarbon radical or a C₁ to C₂₀ unsaturated divalent hydrocarbon radical, R is a C₁ to C₂₀ saturated divalent hydrocarbon radical or a C₁ to C₂₀ unsaturated divalent hydrocarbon radical; (S)_(m) is a divalent group of m sulfur atoms wherein m can be different for each group and represents a whole number of from 1 to about 6 with at least m in one group being at least 2; and x is a whole number ranging from 0 to
 10. 7. A mother solution according to claim 1 or 2, wherein the copolymer has an average viscosimetric molecular weight comprised between 70,000 and 200,000.
 8. A road surface covering according to claim 6 wherein the copolymer is selected from random and block copolymers of styrene with a conjugated diene, selected from butadiene, isoprene chloroprene, carboxylated butadiene, and carboxylated isoprene.
 9. A road surface covering according to claim 6 wherein the copolymer has a weight content of styrene ranging from 15% to 40%.
 10. A road surface covering according to claim 6 wherein the copolymer has an average viscosimetric molecular weight comprised between 30,000 and 300,000.
 11. A road surface covering according to claim 6 wherein the copolymer has an average viscosimetric molecular weight comprised between about 70,000 and 200,000.
 12. A road surface covering according to claim 6 wherein the polysulfide is defined by the formula

    R.sub.1 --(S).sub.n --R.sub.2

wherein R₁ and R₂ each represent a C₁ to C₂₀ saturated monovalent hydrocarbon radical or a C₁ to C₂₀ unsaturated hydrocarbon radical, or R₁ and R₂ can be linked together to form a C₁ to C₂₀ saturated divalent hydrocarbon radical or an unsaturated divalent hydrocarbon radical; --(S)_(n) -- represents a divalent group of n sulphur atoms; n being an integer of from 2 to
 6. 13. A road surface covering according to claim 6 whereinR₁ and R₂ are identical and selected from C₁ to C₂₀ alkyl radicals, C₆ to C₂₀ aryl radicals and C₆ to C₂₀ cycloalkyl radicals or are linked together to form a C₁ to C₂₀ divalent alkylene radical, a C₆ to C₂₀ cycloalkylene or a C₆ to C₂₀ arylene radical, and wherein R is selected from C₁ to C₂₀ alkylene radicals, C₆ to C₂₀ cycloalkylene radicals and C₆ to C₂₀ arylene radicals.
 14. A road surface covering according to claim 6 wherein the polysulphide has the formula:

    R.sub.3 --(S).sub.p --R.sub.3

wherein: R₃ is a C₆ to C₁₆ alkyl radical; and, --(S)_(p) -- represents a divalent group of p sulphur atoms, being an integer of from 2 to
 5. 15. A road surface covering according to claim 6, wherein the copolymer and the polysulphide are added to the bitumen as a mother solution comprising a hydrocarbon oil having a distillation range, at atmospheric pressure comprised between 100° C. and 450° C., and in solution in the copolymer and from about 0.1 to 15% by weight of the oil of the polysulphide.
 16. A mother solution according to claim 1 or 2, wherein the copolymer is selected from random and block copolymers of styrene with a conjugated diene, selected from butadiene, isoprene chloroprene, carboxylated butadiene, and carboxylated isoprene.
 17. A mother solution according to claim 1 or 2, wherein the copolymer has a weight content of styrene ranging from 15% to 40%.
 18. A mother solution according to claim 1 or 2, wherein the copolymer has an average viscosimetric molecular weight comprised between 30,000 and 300,000.
 19. A mother solution according to claim 1 or 2, wherein the hydrocarbon oil has a distillation range, at atmospheric pressure, between 150° C. and 370° C.
 20. A mother solution according to claim 1 or 2, wherein the hydrocarbon oil is selected from petroleum cuts having an aromatic character, the petroleum cuts having a naphteno-paraffin character, petroleum cuts having a naphteno-aromatic character, coal oils, and oils of vegetable origin.
 21. A mother solution according to claim 1 or 2, containing from 10 to 35% copolymer and 0.5 to 5% polysulphide expressed by weight of the hydrocarbon oil.
 22. A mother solution according to claim 1 or 2, prepared by contacting the hydrocarbon oil, copolymer and polysulphide with stirring, at a temperature between 20° and 170° C. 